FIR: Select most specific members from supertypes scope

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/AbstractFirOverrideScope.kt

@@ -25,7 +25,7 @@ abstract class AbstractFirOverrideScope(val session: FirSession, protected val o
         return overrideChecker.isOverriddenProperty(overrideCandidate, baseDeclaration)
     }
 
-    private fun similarFunctionsOrBothProperties(
+    protected fun similarFunctionsOrBothProperties(
         overrideCandidate: FirCallableMemberDeclaration<*>,
         baseDeclaration: FirCallableMemberDeclaration<*>
     ): Boolean {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirAbstractOverrideChecker.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.fir.scopes.impl
 
+import org.jetbrains.kotlin.fir.declarations.FirCallableMemberDeclaration
 import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
 import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
@@ -20,12 +21,7 @@ abstract class FirAbstractOverrideChecker : FirOverrideChecker {
         overrideCandidate: FirSimpleFunction,
         baseDeclaration: FirSimpleFunction
     ): ConeSubstitutor? {
-        if (overrideCandidate.typeParameters.size != baseDeclaration.typeParameters.size) return null
+        val substitutor = buildSubstitutorForOverridesCheck(overrideCandidate, baseDeclaration) ?: return null
-
-        val types = baseDeclaration.typeParameters.map {
-            ConeTypeParameterTypeImpl(it.symbol.toLookupTag(), false)
-        }
-        val substitutor = substitutorByMap(overrideCandidate.typeParameters.map { it.symbol }.zip(types).toMap())
         if (!overrideCandidate.typeParameters.zip(baseDeclaration.typeParameters).all { (a, b) ->
                 a.bounds.size == b.bounds.size && a.bounds.zip(b.bounds).all { (aBound, bBound) ->
                     isEqualTypes(aBound, bBound, substitutor)
@@ -34,4 +30,16 @@ abstract class FirAbstractOverrideChecker : FirOverrideChecker {
         ) return null
         return substitutor
     }
-}
+}
+
+fun buildSubstitutorForOverridesCheck(
+    overrideCandidate: FirCallableMemberDeclaration<*>,
+    baseDeclaration: FirCallableMemberDeclaration<*>
+): ConeSubstitutor? {
+    if (overrideCandidate.typeParameters.size != baseDeclaration.typeParameters.size) return null
+
+    val types = baseDeclaration.typeParameters.map {
+        ConeTypeParameterTypeImpl(it.symbol.toLookupTag(), false)
+    }
+    return substitutorByMap(overrideCandidate.typeParameters.map { it.symbol }.zip(types).toMap())
+}

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirSuperTypeScope.kt

@@ -5,14 +5,28 @@
 
 package org.jetbrains.kotlin.fir.scopes.impl
 
+import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.declarations.FirCallableMemberDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirProperty
+import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
 import org.jetbrains.kotlin.fir.scopes.FirOverrideChecker
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.scopes.ProcessorAction
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassifierSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirConstructorSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirFunctionSymbol
+import org.jetbrains.kotlin.fir.types.ConeFlexibleType
+import org.jetbrains.kotlin.fir.types.ConeKotlinType
+import org.jetbrains.kotlin.fir.types.ConeTypeCheckerContext
+import org.jetbrains.kotlin.fir.types.coneTypeSafe
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.types.AbstractTypeChecker
+import org.jetbrains.kotlin.types.AbstractTypeCheckerContext
+import org.jetbrains.kotlin.utils.addToStdlib.flattenTo
+import java.util.*
+import kotlin.collections.HashSet
 
 class FirSuperTypeScope private constructor(
     session: FirSession,
@@ -26,6 +40,8 @@ class FirSuperTypeScope private constructor(
 
     private val absentClassifiers = mutableSetOf<Name>()
 
+    private val typeContext = ConeTypeCheckerContext(isErrorTypeEqualsToAnything = false, isStubTypeEqualsToAnything = false, session)
+
     override fun processFunctionsByName(name: Name, processor: (FirFunctionSymbol<*>) -> ProcessorAction): ProcessorAction {
         processCallablesByName(name, processor, absentFunctions, FirScope::processFunctionsByName)?.let { return it }
         return super.processFunctionsByName(name, processor)
@@ -46,32 +62,161 @@ class FirSuperTypeScope private constructor(
             return ProcessorAction.NEXT
         }
 
-        val accepted = HashSet<FirCallableSymbol<*>>()
+        val membersByScope = scopes.mapNotNull { scope ->
-        val pending = mutableListOf<FirCallableSymbol<*>>()
+            val resultForScope = mutableListOf<D>()
-        var empty = true
+            scope.processCallables(name) {
-        for (scope in scopes) {
+                if (it !is FirConstructorSymbol) {
-            if (scope.processCallables(name) {
+                    resultForScope.add(it)
-                    empty = false
+                }
-                    if (it !in accepted && it.getOverridden(accepted) == null) {
+                ProcessorAction.NEXT
-                        pending += it
-                        processor(it)
-                    } else {
-                        ProcessorAction.NEXT
-                    }
-                }.stop()
-            ) {
-                return ProcessorAction.STOP
             }
-            accepted += pending
+
-            pending.clear()
+            resultForScope.takeIf { it.isNotEmpty() }
         }
-        if (empty) {
+
-            absentNames += name
+        if (membersByScope.isEmpty()) {
+            absentNames.add(name)
+            return null
+        }
+
+        membersByScope.singleOrNull()?.let { members ->
+            for (member in members) {
+                if (processor(member).stop()) return ProcessorAction.STOP
+            }
+
+            return ProcessorAction.NEXT
+        }
+
+        val allMembers = membersByScope.flattenTo(LinkedList())
+
+        while (allMembers.isNotEmpty()) {
+            val maxByVisibility = findMemberWithMaxVisibility(allMembers)
+            val extractedOverrides = extractBothWaysOverridable(maxByVisibility, allMembers)
+
+            val mostSpecific = selectMostSpecificMember(extractedOverrides)
+
+            if (processor(mostSpecific).stop()) return ProcessorAction.STOP
         }
 
         return null
     }
 
+    private fun <D : FirCallableSymbol<*>> selectMostSpecificMember(
+        overridables: Collection<D>
+    ): D {
+        require(overridables.isNotEmpty()) { "Should have at least one overridable descriptor" }
+        if (overridables.size == 1) {
+            return overridables.first()
+        }
+
+        val candidates: MutableCollection<D> = ArrayList(2)
+        var transitivelyMostSpecific: D = overridables.first()
+
+        for (candidate in overridables) {
+            if (overridables.all { isMoreSpecific(candidate, it) }) {
+                candidates.add(candidate)
+            }
+
+            if (isMoreSpecific(candidate, transitivelyMostSpecific) && !isMoreSpecific(transitivelyMostSpecific, candidate)) {
+                transitivelyMostSpecific = candidate
+            }
+        }
+
+        when {
+            candidates.isEmpty() -> {
+                return transitivelyMostSpecific
+            }
+            candidates.size == 1 -> {
+                return candidates.first()
+            }
+            else -> {
+                candidates.firstOrNull {
+                    val type = it.fir.returnTypeRef.coneTypeSafe<ConeKotlinType>()
+                    type != null && type !is ConeFlexibleType
+                }?.let { return it }
+                return candidates.first()
+            }
+        }
+    }
+
+    private fun isMoreSpecific(
+        a: FirCallableSymbol<*>,
+        b: FirCallableSymbol<*>
+    ): Boolean {
+        val aFir = a.fir
+        val bFir = b.fir
+        if (aFir !is FirCallableMemberDeclaration<*> || bFir !is FirCallableMemberDeclaration<*>) return false
+
+        val substitutor = buildSubstitutorForOverridesCheck(aFir, bFir) ?: return false
+
+        val aReturnType = a.fir.returnTypeRef.coneTypeSafe<ConeKotlinType>()?.let(substitutor::substituteOrSelf) ?: return false
+        val bReturnType = b.fir.returnTypeRef.coneTypeSafe<ConeKotlinType>() ?: return false
+
+        if (aFir is FirSimpleFunction) {
+            require(bFir is FirSimpleFunction) { "b is " + b.javaClass }
+            return isTypeMoreSpecific(aReturnType, bReturnType)
+        }
+        if (aFir is FirProperty) {
+            require(bFir is FirProperty) { "b is " + b.javaClass }
+            // TODO: if (!OverridingUtil.isAccessorMoreSpecific(pa.getSetter(), pb.getSetter())) return false
+            return if (aFir.isVar && bFir.isVar) {
+                AbstractTypeChecker.equalTypes(typeContext as AbstractTypeCheckerContext, aReturnType, bReturnType)
+            } else { // both vals or var vs val: val can't be more specific then var
+                !(!aFir.isVar && bFir.isVar) && isTypeMoreSpecific(aReturnType, bReturnType)
+            }
+        }
+        throw IllegalArgumentException("Unexpected callable: " + a.javaClass)
+    }
+
+    private fun isTypeMoreSpecific(a: ConeKotlinType, b: ConeKotlinType): Boolean =
+        AbstractTypeChecker.isSubtypeOf(typeContext as AbstractTypeCheckerContext, a, b)
+
+    private fun <D : FirCallableSymbol<*>> findMemberWithMaxVisibility(members: Collection<D>): D {
+        assert(members.isNotEmpty())
+
+        var member: D? = null
+        for (candidate in members) {
+            if (member == null) {
+                member = candidate
+                continue
+            }
+
+            val result = Visibilities.compare(
+                (member.fir as FirCallableMemberDeclaration<*>).status.visibility,
+                (candidate.fir as FirCallableMemberDeclaration<*>).status.visibility
+            )
+            if (result != null && result < 0) {
+                member = candidate
+            }
+        }
+        return member!!
+    }
+
+    private fun <D : FirCallableSymbol<*>> extractBothWaysOverridable(
+        overrider: D,
+        members: MutableCollection<D>
+    ): Collection<D> {
+        val result = mutableListOf<D>().apply { add(overrider) }
+
+        val iterator = members.iterator()
+
+        val overrideCandidate = overrider.fir as FirCallableMemberDeclaration<*>
+        while (iterator.hasNext()) {
+            val next = iterator.next()
+            if (next == overrider) {
+                iterator.remove()
+                continue
+            }
+
+            if (similarFunctionsOrBothProperties(overrideCandidate, next.fir as FirCallableMemberDeclaration<*>)) {
+                result.add(next)
+                iterator.remove()
+            }
+        }
+
+        return result
+    }
+
     override fun processClassifiersByName(name: Name, processor: (FirClassifierSymbol<*>) -> ProcessorAction): ProcessorAction {
         if (name in absentClassifiers) {
             return ProcessorAction.NEXT

compiler/fir/resolve/testData/resolve/overrides/simpleMostSpecific.kt

@@ -0,0 +1,41 @@
+// !CHECK_TYPE
+interface A {
+    val x: CharSequence
+
+    fun foo(): String?
+
+    fun <T, F> bar(x: T, y: F): F?
+}
+
+interface B {
+    var x: String
+
+    fun foo(): String
+
+    fun <X, Y> bar(x: X, y: Y): Y
+}
+
+interface C {
+    val x: String
+}
+
+interface D1 : A, B
+interface D2 : B, A
+interface D3 : A, C
+
+fun main(d1: D1, d2: D2, d3: D3) {
+    d1.x.checkType { _<String>() }
+    d1.x = ""
+    d1.foo().checkType { _<String>() }
+    d1.bar(1, "").checkType { _<String>() }
+
+    d2.x.checkType { _<String>() }
+    d2.x = ""
+    d2.foo().checkType { _<String>() }
+    d2.bar(1, "").checkType { _<String>() }
+
+    d3.x.checkType { _<String>() }
+    d3.x = ""
+    d3.foo().checkType { _<String?>() }
+    d3.bar(1, "").checkType { _<String?>() }
+}

compiler/fir/resolve/testData/resolve/overrides/simpleMostSpecific.txt

@@ -0,0 +1,86 @@
+FILE: simpleMostSpecific.kt
+    public abstract interface A : R|kotlin/Any| {
+        public abstract val x: R|kotlin/CharSequence|
+            public get(): R|kotlin/CharSequence|
+
+        public abstract fun foo(): R|kotlin/String?|
+
+        public abstract fun <T, F> bar(x: R|T|, y: R|F|): R|F?|
+
+    }
+    public abstract interface B : R|kotlin/Any| {
+        public abstract var x: R|kotlin/String|
+            public get(): R|kotlin/String|
+            public set(value: R|kotlin/String|): R|kotlin/Unit|
+
+        public abstract fun foo(): R|kotlin/String|
+
+        public abstract fun <X, Y> bar(x: R|X|, y: R|Y|): R|Y|
+
+    }
+    public abstract interface C : R|kotlin/Any| {
+        public abstract val x: R|kotlin/String|
+            public get(): R|kotlin/String|
+
+    }
+    public abstract interface D1 : R|A|, R|B| {
+    }
+    public abstract interface D2 : R|B|, R|A| {
+    }
+    public abstract interface D3 : R|A|, R|C| {
+    }
+    public final fun main(d1: R|D1|, d2: R|D2|, d3: R|D3|): R|kotlin/Unit| {
+        R|<local>/d1|.R|/B.x|.R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d1|.R|/B.x| = String()
+        R|<local>/d1|.R|/B.foo|().R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d1|.R|/B.bar|<R|kotlin/Int|, R|kotlin/String|>(Int(1), String()).R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d2|.R|/B.x|.R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d2|.R|/B.x| = String()
+        R|<local>/d2|.R|/B.foo|().R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d2|.R|/B.bar|<R|kotlin/Int|, R|kotlin/String|>(Int(1), String()).R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d3|.R|/C.x|.R|tests/_checkType/checkType|<R|kotlin/String|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String|>()
+        }
+        )
+        R|<local>/d3|.R|/C.x| = String()
+        R|<local>/d3|.R|/A.foo|().R|tests/_checkType/checkType|<R|kotlin/String?|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String?>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String?|>()
+        }
+        )
+        R|<local>/d3|.R|/A.bar|<R|kotlin/Int|, R|kotlin/String|>(Int(1), String()).R|tests/_checkType/checkType|<R|kotlin/String?|>(<L> = checkType@fun R|tests/_checkType/Inv<kotlin/String?>|.<anonymous>(): R|kotlin/Unit| {
+            this@R|special/anonymous|.R|tests/_checkType/_|<R|kotlin/String?|>()
+        }
+        )
+    }
+FILE: CHECK_TYPE.kt
+    public final fun <T> checkSubtype(t: R|T|): R|T| {
+        ^checkSubtype R|<local>/t|
+    }
+    public final class Inv<T> : R|kotlin/Any| {
+        public constructor<T>(): R|tests/_checkType/Inv<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+    }
+    public final fun <E> R|tests/_checkType/Inv<E>|._(): R|kotlin/Unit| {
+    }
+    public final infix fun <T> R|T|.checkType(f: R|tests/_checkType/Inv<T>.() -> kotlin/Unit|): R|kotlin/Unit| {
+    }

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java

@@ -873,6 +873,11 @@ public class FirDiagnosticsTestGenerated extends AbstractFirDiagnosticsTest {
             runTest("compiler/fir/resolve/testData/resolve/overrides/simpleFakeOverride.kt");
         }
 
+        @TestMetadata("simpleMostSpecific.kt")
+        public void testSimpleMostSpecific() throws Exception {
+            runTest("compiler/fir/resolve/testData/resolve/overrides/simpleMostSpecific.kt");
+        }
+
         @TestMetadata("supertypeGenerics.kt")
         public void testSupertypeGenerics() throws Exception {
             runTest("compiler/fir/resolve/testData/resolve/overrides/supertypeGenerics.kt");

compiler/testData/ir/irText/expressions/kt30020.fir.txt

@@ -201,10 +201,10 @@ FILE fqName:<root> fileName:/kt30020.kt
       overridden:
         public abstract fun isEmpty (): kotlin.Boolean declared in kotlin.collections.List
       $this: VALUE_PARAMETER name:<this> type:kotlin.collections.List
-    FUN FAKE_OVERRIDE name:iterator visibility:public modality:ABSTRACT <> ($this:kotlin.collections.List) returnType:kotlin.collections.Iterator<kotlin.Int> [fake_override,operator]
+    FUN FAKE_OVERRIDE name:iterator visibility:public modality:ABSTRACT <> ($this:kotlin.collections.MutableCollection) returnType:kotlin.collections.MutableIterator<kotlin.Int> [fake_override,operator]
       overridden:
-        public abstract fun iterator (): kotlin.collections.Iterator<E of kotlin.collections.MutableList> [operator] declared in kotlin.collections.List
+        public abstract fun iterator (): kotlin.collections.MutableIterator<E of kotlin.collections.MutableList> [operator] declared in kotlin.collections.MutableCollection
-      $this: VALUE_PARAMETER name:<this> type:kotlin.collections.List
+      $this: VALUE_PARAMETER name:<this> type:kotlin.collections.MutableCollection
     FUN FAKE_OVERRIDE name:lastIndexOf visibility:public modality:ABSTRACT <> ($this:kotlin.collections.List, element:kotlin.Int) returnType:kotlin.Int [fake_override]
       overridden:
         public abstract fun lastIndexOf (element: E of kotlin.collections.MutableList): kotlin.Int declared in kotlin.collections.List